1. Field of the Invention
This invention relates to an insulation-film etching system that etches an insulation-film on a substrate.
2. Description of the Related Art
Surface processes onto a substrate are widely practical in manufacturing such electronic devices as LSIs (Large-Scale Integrated circuits) and LCDs (Liquid Crystal Displays). Among them, a process to etch an insulation-film on a substrate is one of key processes in micro-circuit formation. For example, a coated resist is patterned on an insulation-film such as silicon oxide film or silicon nitride film covering a silicon wafer. The insulation-film is etched using the patterned resist as “mask”. Then, a micro-circuit is formed by burying metal such as tungsten or aluminum into the etched parts. Though the term “substrate” means a board-shaped base for a product, one composed of a board-shaped base and any layer or film formed is sometimes called “substrate” as a whole in this specification.
Dry etching utilizing plasma is popular among insulation-film etching systems. In this type of system, a gas is introduced into a process chamber, and plasma is generated by a HF (High-Frequency) discharge. The introduced gas is reactive one such as CHF3 so that the RIE (Reactive Ion Etching) can be carried out by function of activated or ionized species produced in the plasma. Though “HF” usually means frequencies ranging from 3 MHz to 30 MHz, “HF” in this specification broadly means frequencies higher than MF (Medium Frequency, 300 kHz to 3000 kHz), including VHF (Very High Frequency, 30 MHz to 300 MHz) and UHF (Ultra High Frequency, 300 MHz to 3000 MHz).
At the background that higher function, larger-scale integration and higher performance are consistently required to electronic devices as products, requirement to etching systems has become severer and severer. Especially, higher cleanness of atmosphere in process chambers is more severely required at the background that circuits are made finer and finer. In this respect, what matters in insulation-film etching systems is film deposition in process chambers, which is caused from a gas used for etching. This point will be described as follows, taking the silicon-oxide-film etching as an example.
In the silicon-oxide-film etching, plasma is generated of a fluorohydrocarbon gas such as CHF3. Fluorine decomposing in the fluorohydrocarbon plasma reacts with silicon, producing volatile SiF4. The etching is carried out as the silicon oxide film is transformed to volatile material by such the reaction. In this type of the etching utilizing a fluorohydrocarbon gas, however, a carbon-series film might be easily deposited on an exposed surface in the process chamber during the etching under the influence of unreacting or undecomposing species. The film deposition might also take place from a residual gas after the etching. The deposited film in the etching using such a fluorohydrocarbon gas is polymer composed of fluorine, carbon and hydrogen.
The film deposited on the exposed surface in the process chamber may peel off from its internal stress or weight. When this happens, particles of some extent size are released. If the particles are attached on the substrate to be processed, critical defects such as breaking or short of the circuit may take place. In addition, when the particles are attached on a substrate holder, there arises the problem that contact of the substrate onto the substrate holder becomes worse in the next etching. At worse contact of the substrate onto the substrate holder, the temperature of the substrate may be unstable or out of uniform during the etching, leading to deterioration of the etching property.
Particularly at the background of recent demand to further enhance integration levels and functions of products, some gases having various functions are often mixed. The mixed gases tend to promote the film depositions. On the other hand, amount of released particles, which affect the etching processes, are required to be as small as possible. In a sense, severe requirements conflicting to each other are subjected to the etching systems.